Field of the Invention
The present invention relates to an optical filter and an imaging device including the same.
Background Art
Imaging devices such as cameras use a CMOS sensor to convert incident light into electronic signals, thereby forming images. To realize high-quality images with the high pixel counts of the cameras, a newly developed back side illuminated-type (BSI-type) CMOS sensor has been applied to main cameras instead of a front side illuminated-type (FSI-type) CMOS sensor. The FSI-type CMOS sensor has an effect of blocking out some of the light since wirings are formed on a top surface of a photodiode (PD). On the other hand, the BSI-type CMOS sensor may receive a larger amount of incident light compared to the FSI-type CMOS sensor since the wirings are disposed under the photodiode to receive a larger amount of light, and thus has an effect of increasing the intensity of an image by 70% or more. Therefore, the BSI-type CMOS sensors are generally applied in most cameras with over eight million pixels.
Such a BSI-type CMOS sensor has a structure in which light having a larger angle of incidence can reach the photodiode, compared to that in the FSI-type CMOS sensor.
In general, the CMOS sensor may also detect light in a wavelength region which cannot be seen by the naked eye. Since an image is distorted by the light in such a wavelength region, colors different from those viewed by the naked eye are observed. To solve this problem, an optical filter is used in the front of the CMOS sensor. However, the conventional optical filter has a problem in that the transmission spectrum of the optical filter varies as the angle of incidence of light varies, thereby resulting in distorted images.